mjhjmtu

I've just set up a Debian system to try out a couple of projects and improve my understanding of Linux but I'm running into problems with cryptsetup straight after installation. I used the graphical installer for Debian 9 and used its baked-in encryption tool to encrypt /home and the swap space which I have set up as logical volumes.

I'm trying to change the encryption passphrase for each drive, after I stupidly left caps-lock on after setting up the partitions.

I'd hoped I'd be able to do this simply using cryptsetup luksChangeKey. However, whenever I attempt to access either the devices/containers with cryptsetup (running as root) I seem to get the error:

<device> is not a valid LUKS device.

Please find outputs from lsblk, ls /dev/mapper and cryptsetup below, which I hope give a good indication of how I'm set up and the problems I'm experiencing:

lsblk
NAME MAJ:MIN RM SIZE RO TYPE MOUNTPOINT
sda 8:0 0 111.8G 0 disk 
├─sda1 8:1 0 953M 0 part /boot/efi
├─sda2 8:2 0 477M 0 part /boot
└─sda3 8:3 0 110.4G 0 part 
 ├─SSD1_LVM-LV_ROOT 254:0 0 7.5G 0 lvm /
 ├─SSD1_LVM-LV_VAR 254:1 0 14.9G 0 lvm /var
 ├─SSD1_LVM-LV_TMP 254:2 0 7.5G 0 lvm /tmp
 ├─SSD1_LVM-LV_USR 254:3 0 29.8G 0 lvm /usr
 ├─SSD1_LVM-LV_HOME 254:4 0 7.5G 0 lvm 
 │ └─SSD1_LVM-LV_HOME_crypt 254:8 0 7.5G 0 crypt /home
 ├─SSD1_LVM-LV_OPT 254:5 0 14.9G 0 lvm /opt
 └─SSD1_LVM-LV_SWAP 254:6 0 15.9G 0 lvm 
 └─SSD1_LVM-LV_SWAP_crypt 254:7 0 15.9G 0 crypt 
ls -l /dev/mapper
total 0
crw------- 1 root root 10, 236 Sep 27 09:35 control
lrwxrwxrwx 1 root root 7 Sep 27 09:36 SSD1_LVM-LV_HOME -> ../dm-4
lrwxrwxrwx 1 root root 7 Sep 27 09:36 SSD1_LVM-LV_HOME_crypt -> ../dm-8
lrwxrwxrwx 1 root root 7 Sep 27 09:35 SSD1_LVM-LV_OPT -> ../dm-5
lrwxrwxrwx 1 root root 7 Sep 27 09:35 SSD1_LVM-LV_ROOT -> ../dm-0
lrwxrwxrwx 1 root root 7 Sep 27 09:35 SSD1_LVM-LV_SWAP -> ../dm-6
lrwxrwxrwx 1 root root 7 Sep 27 15:50 SSD1_LVM-LV_SWAP_crypt -> ../dm-7
lrwxrwxrwx 1 root root 7 Sep 27 09:35 SSD1_LVM-LV_TMP -> ../dm-2
lrwxrwxrwx 1 root root 7 Sep 27 09:35 SSD1_LVM-LV_USR -> ../dm-3
lrwxrwxrwx 1 root root 7 Sep 27 09:35 SSD1_LVM-LV_VAR -> ../dm-1
cryptsetup status /dev/dm-7
/dev/dm-7 is active.
 type: LUKS1
 cipher: aes-xts-plain64
 keysize: 512 bits
 device: /dev/mapper/SSD1_LVM-LV_SWAP
 offset: 4096 sectors
 size: 33198080 sectors
 mode: read/write
cryptsetup luksAddKey /dev/dm-7
Device /dev/dm-7 is not a valid LUKS device.

I disabled disk swap space with swapoff in case that was causing problems, which regrettably hasn't helped.

You have to run cryptsetup on the device that holds the LUKS header (for actions that modify the header, i.e. format, key management, dump, ...).

In your case, this is /dev/mapper/SSD1_LVM-LV_SWAP

But you tried to run it on /dev/mapper/SSD1_LVM-LV_SWAP_crypt which is the swap LV (encrypted) and presumably holds a swap header (mkswap) instead of a LUKS header (that would be luks inside luks...).